Known test methods and systems for measuring and testing analog circuits on electronic circuit boards require the use of expensive external test equipment and signal node probing mechanisms. During test, the analog circuits operate together functionally while an external analog tester probes, stores and processes analog signals within the analog circuit. These external analog test systems do not provide the capability to easily monitor the analog signals while the analog circuitry operates normally in its system environment due to limited physical access to probe the circuit nodes. Moreover, known analog test methods are not easily useable during the entire life cycle of a functional circuit, i.e., during production test, system integration, system test, on-line test or diagnostics, and field support and maintenance.
A particular limitation associated with traditional analog test methods is that state of the art board designs are so densely populated with integrated circuits that physical probing of the analog signals is very difficult, if not impossible. Moreover, in traditional systems the necessity for external probes to make contact with the signal path often affects the analog signal. Probes add resistive and capacitive loads to an analog signal that potentially cause the signal characteristics (e.g., voltage amplitude and wave shape) to change when these systems take voltage measurements. As a result, physical probing of analog signals can produce inaccurate measurements and distort test results.
Yet another problem associated with traditional test methods is that these tests are dependent on the availability of external testers and probing fixtures. These systems usually include complex and cumbersome electronic circuits housed within various cabinets or component chassis. In a field environment, the transportation and upkeep of these components can be a very expensive proposition.
At an even more detailed level, even if a solution to the above problems were available, the most effective and efficient method to output multiple digitized analog patterns from any test circuit for these purposes is that provided by IEEE standard 1149.1. That standard, describes the execution of a data register scan cycle that can be used for analog signal monitoring operations and requires that for each digitized analog pattern monitored a complete data register scan cycle be performed. In each data register scan cycle, selection, data capture, data shifting, data updating, and other operations are necessary. If there were a way to eliminate the need to perform a complete data register scan cycle for each digitized analog pattern accessed, it may be possible to significantly decrease the amount of time taken to test each analog circuit.
Therefore, there is a need for an analog test method that does not rely on the availability of test equipment in a field environment.
There is a need for an analog signal testing method and circuit that does not include the resistive and capacitive loads that distort signal characteristics during testing.
There is a further need for an analog test method and circuit that efficiently uses a data register scan cycle for accessing digitized analog patterns during testing.